1. Field of the Invention
The present invention relates to a laser light beam generating apparatus. More particularly, the present invention relates to a laser light beam generating apparatus producing a laser light beam wavelength-converted by a non-linear optical crystal device.
2. Background of the Invention
In Japanese Laid-Open Utility Model Publication No. 48-93784 for example, a laser light beam generating apparatus utilizing an efficient wavelength conversion such as second harmonics generation (SHG) is disclosed. The laser light beam generating apparatus emits a short wavelength laser light beam or a wavelength-converted laser light beam by a non-linear optical crystal device and uses a laser light beam of fundamental frequency with high power density within a laser resonator.
A conventional laser light beam generating apparatus utilizing the efficient wavelength conversion includes a light beam source and a resonator having a laser medium and a non-linear optical device element. At least one pumping light beam emitted from the light beam source is irradiated to the laser medium of the resonator. The laser medium is excited by the pumping light beam and generates a laser light beam of fundamental frequency. The laser light beam of fundamental frequency generated from the laser medium is irradiated to the non-linear optical device element. As a result, a SHG laser light beam is generated from the non-linear optical crystal device and outputted from the resonator.
For assembling and using the laser light beam generating apparatus utilized the efficient wavelength conversion in various equipment, such as an optical disc recording and/or reproducing apparatus or other like, it is desirable that optical elements necessary for the SHG laser light beam emission be housed within a small-sized case for facilitated handling as a component.
In general, for stably obtaining an SHG laser light beam with high efficiency in the above mentioned laser light beam generating apparatus, it is necessary that the pumping light beam from the light beam source such as a laser diode is efficiently absorbed in the laser medium such as Nd:YAG. It is also necessary that temperature is controlled within a limited range allowing stable operation with little noise, for such reason as changes in temperature dependence of the phase delay quantity and longitudinal mode of the non-linear optical crystal device of the resonator. For pumping light beam to be efficiently absorbed in the laser medium, it is necessary to adjust the wavelength of the laser medium, and since the wavelength of the pumping light beam changes in accordance with the temperature of the light beam .source such as the laser diode, it is necessary to temperature-control the light beam source.
Since it is thus necessary to perform temperature control of the resonator and the light beam source, two systems of temperature-control and two systems of temperature detection are necessary, thereby complicating the construction and consequently causing a problem of increasing power consumption. In particular, in a laser light beam generating apparatus including the optical elements for laser light beam emission and temperature-control device housed in a small-sized case, when the light beam source and resonator are each arranged on a separate temperature-control device, adjustment of the positions of the light beam source and the resonator to each other becomes difficult, as their relative position shifts in accordance with changes in temperature, thereby causing a problem of unstable operation.
On the other hand, when a laser light beam generating apparatus utilizing the efficient wavelength conversion, having an SHG laser light beam emitting optical system housed within a small-sized case, is to be assembled into various equipment, such as an optical disc recording and/or reproducing apparatus, it is necessary to perform so-called optical axis matching, which operation preferably may be performed without excessive difficulties. The optical axis matching is carried out by fine adjustment in two perpendicular directions on a surface perpendicular to the optical axis. However, the devices of the SHG laser light beam generating optical system are arranged in a direction parallel to the bottom surface of the case such as a horizontal surface, with the direction of the optical axis being parallel to the bottom surface of the case as the horizontal surface. Since the bottom surface as the horizontal surface is usually attachment surface of the laser light beam generating apparatus, one of the two perpendicular directions for optical axis matching is perpendicular to the attachment surface. Because of the perpendicular movement relative to the attachment surface of the case, the arrangement for fine adjustment operation become troublesome while it is difficult to raise operating accuracy.